1. Field of the Invention
The present invention relates to a liquid crystal display that reduces a response time for obtaining a desired luminance.
2. Description of Related Art
A liquid crystal display (LCD) includes a pair of panels including a pixel electrode and a common electrode and a liquid crystal (LC) layer interposed between the panels and having dielectric anisotropy. The pixel electrode is arranged in a matrix and connected to switching elements, such as thin film transistors (TFTs). The pixel electrode is supplied with data voltages through the TFTs, e.g., row by row. The common electrode is arranged on an entire surface of a panel. The pixel electrode, the common electrode, and the LC layer disposed therebetween form a LC capacitor. The LC capacitor and the switching element are basic elements of the pixel.
The LCD generates an electric field in the LC layer when a voltage is applied to the electrodes. Desired images are obtained by controlling a strength of the electric field such that a transmittance of light that is incident upon the LC layer varies.
Among the LCDs, a vertical alignment (VA) mode LCD, which aligns LC molecules such that the long axes of the LC molecules are perpendicular to the panels in absence of an electric field, is discussed herein because the VA mode LCD has a high contrast ratio and wide viewing angle.
The viewing angle of the VA mode LCD may be realized by forming cutouts in the field-generating electrodes and forming protrusions on the field-generating electrodes. The cutouts and the protrusions affect the tilt directions of the LC molecules.
The response time of the liquid crystal is important because an increased size and the resolution of the LCD display device requires a faster response time than is currently being provided.
In detail, it takes longer for a pixel to reach a desired luminance when the response time of the LC is slow. The time for obtaining the desired luminance depends on a difference between a target voltage for giving the desired luminance and a previously charged voltage across the LC capacitor of the pixel. The pixel may not reach the desired luminance for a given time when the voltage difference is large.
To solve the above identified problem, dynamic capacitance compensation (DCC) may be used. DCC improves the response time of the LC without changing the characteristics of the LC. The DCC applies a higher voltage than the target voltage to the LC capacitor to reduce the time for pixel to reach a desired luminance.
However, applying a high voltage to the LC molecules in a cutout-type VA mode LCD causes them to be partially out of order. As such, the response time may not be reduced and the display characteristics of the LCD may deteriorate.
Accordingly, the LC molecules should be pre-tilted before applying the high voltage. For example, one conventional pre-tilting technique is performed by comparing image signals of three successive frames, however, this requires that the number of frame memories be increased, which increases the cost and delays the time for displaying an image. Another conventional pre-tilting technique deforms the pixel structure of the LCD, which decreases the contrast ratio and complicates the manufacturing process.